1. Field of the Invention
This invention relates to devices for counterbalancing free inertial forces in internal combustion, reciprocating-piston, crankshaft engines.
2. Description of Related Art
Internal combustion piston engines include a crankshaft that rotates in a crankcase about a crankshaft axis. A reciprocating piston connects to a piston connecting rod, which, in turn, pivotally connects to the crankshaft at a piston connecting rod axis.
Operation of such conventional engines creates vibrations in the engine. The magnitude of these vibrations depends on the underlying design concept of engine and on the principle according to which it operates (two-cycle, four-cycle). The orientation and magnitude of these vibrations also depend on the number of cylinders and on how the individual cylinders are arranged relative to each other. Internal combustion engines that have a large number of cylinders usually have very good mass compensation for the crankshaft drive forces and moments, so that such engines seldom require mass compensation to balance the inertial forces. In order to keep the inertial forces as small as possible in an internal combustion engine that has only a small number of cylinders, on the other hand, one or a plurality of counterweights are arranged within the crankcase in such a way that they balance out the inertial forces of the engine very precisely by operating at the same frequency (or a multiple thereof), but phase-shifted through 180 degrees. This means that when the piston moves downwards, the counterweight moves upwards and vice versa.
U.S. Pat. No. 4,819,593 discloses one such counterbalancing system. A counterweight pivotally connects to a crankcase and to a counterweight connecting rod/link. The counterweight connecting rod, in turn, pivotally connects to the crankshaft for relative rotation about a counterweight connecting rod axis. Rotation of the crankshaft drives the counterweight 180 degrees out of phase. Consequently, the crankshaft axis, connecting rod axis, and counterweight connecting rod axis are coplanar.
Conventional counterbalancing systems often include many moving parts and are expensive to construct and maintain. While conventional mass balancing systems reduce engine vibrations, they do not totally eliminate all engine vibration.